Yesterday Anne talked to us about the geology and early settlement along the river Thames, providing insights into the early development of the Thames Basin and the first communities in London.
The Thames lies within a chalk trough with North Downs to the south and the Chiltern Hills to the north.
During the Cretaceous period Britain was still connected to Europe, Greenland and North America by 60 metres of impermeable Gault Clays sat on Paleozoic mud and sandstones. Above these clays were some greensand and a bed of white chalk about 200 metres thick. London was still under warm tropical seas 50-60 million years ago and when the waters receded they left rich deposits of London Clay. This clay supports most of the deep foundations and tunnels under London.
The origin of the Thames river system was much further north, almost opposite the Rhine. The impact of the southerly movement of the last Ace Age 110,000 years to 11,000 years ago had the effect of pushing the course of the river to its present position in the south of England.
The river wore down through layers of chalk and some of the London Clay, leaving gravel terraces on its margins. The chalk and clay formed an artesian basin with water trapped under the clay. Keeping the water table in the right place is a balancing act. It was high until, in the 1960s, we took too much out of the basin. The waters in the basin have been allowed to rise again, but not to its natural limits or London’s tunnels and tubes would all be underwater.
The Romans chose their crossing point near modern London bridge as it was relatively shallow and fordable. There were also fairly solid shale deposits on both shores at this point and a small amount of high land on the south (present day Southwark) so a pontoon bridge could be stretched across the water supported both sides of the river. Most of the south of the river was marshy and under water so it took much longer to develop and originally it was full of gardens and pleasure activities, then small piecemeal factories and industries. and not till the building of the City Hall was any Government involvement. This was followed by the construction of the Festival Hall which lead the way to the South Bank Complex.
The river gouges out the outer bends where it is easier for boats to land, so Richmond, Teddington, Twickenham, The City and Westminster, for instance, are all on the outer bends while the inner areas of the bend tend to benefit from fertility and therefore saw the establishment of large public gardens such as the Royal Botanical Gardens at Kew, Richmond Park and Ranelagh Gardens in Chelsea. The Docks manipulated the Thames by running canals and docks through the loops – West India Docks, London Docks, Surrey Docks and, largest of all the London dock networks, the Royal Docks.
The Thames mouth has always been managed to prevent flooding but the shore line still varies and development has not extended there in the same way as the rest of the Thames except for the large power stations and Tilbury docks. It is still awaiting further development.